| Affected by factors such as the multi-scale nature of the cracks in the bedrock and the complexity of the three-dimensional spatial distribution,the groundwater seepage in the bedrock cracks has a strong scale effect,unevenness and anisotropy;Based on the study of the fracture tensor of the fractured rock mass,the simulation and calculation of the groundwater seepage field will give reasonable results such as groundwater dynamics and water volume changes.In the past,most of the researches focused on a specific problem among the above problems,and there was no comprehensive research on multiple problems in the same study area.In this paper,with the fissure scale as the main line,research work is carried out on the above problems,with emphasis on the seepage characteristics of small-scale rough fractures and the permeability of mesoscale fracture networks.This research is supported by the National Natural Science Foundation of China(No.41562017),"Research on groundwater flow simulation based on the three-dimensional spatial distribution of fissures" and the enterprise cooperation project "Hydrogeological survey of Songshujiao Tin Mine in Gejiu City,Yunnan Province" and other projects to carry out topic selection,Data collection,theoretical deduction and thesis writing.The predominant directions of the measured fracture level in the study area are 325° and 75°,and the width of the fracture is between 0.1 and 0.4 mm,which is generally in accordance with the normal distribution.The structural development of the study area divides the area into 12 rock mass blocks,and the development of cracks in the horizontal direction of these blocks has its own characteristics;the width of the cracks in the vertical direction gradually decreases with the elevation,which generally conforms to a linear change.With the help of rock CT technology and three-dimensional laser scanning technology,the scanning of 46 different types of rock samples in the study area was completed,and the three-dimensional morphological data of 17 typical fracture surfaces were extracted.Using the method of controlling the tangential and normal double displacement of the fracture surface,a three-dimensional double-wall rough fracture model of the laser scanning fracture surface is generated.Based on the local cubic law,a three-dimensional fissure width function interpolation seepage simulation method is established,which improves the calculation speed and has good results.Complete the seepage calculation of 15 typical fracture surfaces,and the roughness coefficient ranges from 1.33 to 8.21.The permeability of 40 rock samples in the study area was measured.The average permeability of limestone in the gas measurement method was 7.41E-16m2,and the average permeability of dolomite was 1.04E-15 m2.The permeability is much smaller than the result of the gas measurement method.The simulation of the fracture network uses the GEOFRAC method,which uses the sequential Gaussian simulation method(SGS)to simulate the spatial distribution of the fracture position,the principal component analysis method to simulate the spatial distribution of the fracture direction,and connect the fracture elements according to specific rules to form a three-dimensional fracture surface,and generate 66,812 fissures in 12 sub-regions on the surface and 7632 fissures in 8 sub-regions on the surface are formed;the shape of the fissures adopts a disc model to form a three-dimensional fracture network.Based on the law of conservation of mass,the cross-dimensional coupling control equations of two-dimensional fractured flow and three-dimensional Darcy seepage flow are derived to ensure the continuity of pressure,velocity and mass of the seepage field in the numerical model calculation domain.Using the discrete fracture and matrix(DFM)model,coupling two-dimensional fracture flow and three-dimensional matrix Darcy flow to calculate the seepage tensor of fractured rock masses,complete the calculation of the permeability tensor of 20 DFM models in 12 subregions on the surface and 8 subregions;And use the pumping test results of 2hole groups to verify.The self-programming of the calculation results of the 3D permeability tensor of the fractured rock mass realizes the visualization of the 3D permeability ellipsoid.Based on the second-order symmetric positive definiteness of the permeability tensor,the stability judgment formula of the two-dimensional central difference method for the groundwater flow equation in anisotropic water-bearing medium is derived.The analysis believes that MODFLOW2005 can complete the simulation and calculation of the seepage flow of anisotropic water-containing media under specific conditions,and the calculation speed is fast;but the calculation stability is relatively poor when it is based on a rectangular grid and an explicit difference format.Comparing and analyzing the River and Drain modules,it is more reasonable to use the River model when the roadway's groundwater replenishment needs to be considered;the River and Drain modules cannot respond quickly to changes in water volume;it plays a decisive role in the water volume changes in the River and Drain modules It is the head difference with the aquifer.A simulation of anisotropic aquifer seepage field was carried out in the Gaosong mine field in Gejiu,Yunnan,and the two numerical simulation results of anisotropy and isotropy were compared;the predicted value of roadway water inflow under isotropic conditions was significantly larger than the measured value.The maximum calculation error is 67.10%;the calculation result of the model using the improved permeability tensor as the aquifer permeability parameter is less than 32.23%.The reason for the deviation in numerical calculation of groundwater in anisotropic aquifers is analyzed by using the seepage ellipsoid. |
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